This study was conducted to quantify the likely impacts and benefits of current and futurerndevelopment options in the Blue Nile basin using simulation approach. Four cases studies wererninvestigated under different scenarios; i) the filling strategy of the under-construction GreatrnRenaissance Dam (GERD), ii) the long term GERD operation case study iii) strategicrndevelopment perspective case study that includes all proposed dams upstream of GERD inrnAbbay-Blue Nile and iv) future irrigation development in the Eastern Nile. Mike Basin and MikernHydro River Basin Simulation Models were used.rnThe results indicate 6 years filling period is mostly sufficient to fill the GERD reservoir with nornimpact on the current irrigation water use of Egypt. However, if a rare scenario of 6 years dryrnconsecutive sequence of flow that was observed in the 1980s occurs, the filling strategy need tornbe revised. Analysis of the hypothetical scenarios within -/+ 20 flow variation from the long termrnmean indicates the 6 years filling sequence lower than the normal (mean) flow by up to 10% willrnbe in the tolerable range of filling.rnIn terms of long term analysis, once GERD reservoir is filled and started operation, it imposes nornthreat to the existing agricultural water use on downstream countries (Sudan and Egypt).rnHowever, the annual energy production from HAD may be reduced by 6 to 8% due to thernreduction in the head available at the Dam in Egypt. Overall, the presence of GERD rendersrnmore regional benefit than before. The mean energy in Eastern Nile region could increase byrnmore than 120%. If additional proposed dams are developed as strategic option in the Abbay-rnBlue Nile sub basin, up to 56,000 GWh/year of energy can be produced without significantrnivrnimpact on regional agricultural water uses. The upstream country Ethiopia can generate as muchrnas 38200 GWh of Energy and the energy production in Sudan increases by 38%.rnHowever, expansion of irrigated agriculture in the Eastern Nile basin generally may impact bothrnthe hydropower and existing agricultural water uses downstream of GERD. Analysis based onrnplanned irrigation development in the basin indicates, water availability is a major constraint thatrnlimits irrigated agriculture expansion. The planned irrigation development in Sudan and Ethiopiarnmay reduce water availability for agriculture by as much as 26.3% in the Eastern Nile basin. Thernpossibility of more large-scale irrigation exists in the basin, but it is not close to the extent ofrnplanned development. As the study utilized the planned irrigation development by the countries,rncomprehensive regional planning and coordinated water management scenario, which is notrncovered under this study, may yield a better overview of irrigation expansion in the basin.rnThis study is a comprehensive analysis of the impacts and benefits of hydropower and irrigationrndevelopment in the Eastern Nile basin and may lay a basis for future scientific engagement in thernbasin. Hydropower development in the upper reaches of Abbay-Blue Nile basin is enormous andrnrenders distinct possibility for future development beyond the completion of GERD. However,rnplanned large scale expansion of irrigated agriculture introduces water deficit to both energy andrnagriculture production and requires coordinated regional planning and analysis for optimalrneconomic and social returns to the basin. The future holds a great deal of uncertainty in terms ofrnsocio-economic and political changes that influence development decisions. To take fullrnadvantage of the water resources of the basin it is necessary the basin be managed as a singlernsystem which requires the establishment of an effective institutional mechanism that aim torndevelop the river in a shared-vision and cooperative way. Furthermore, future climate changernmay put additional uncertainties to the Eastern Nile basin development. Therefore, it is suggestedrnthat analysis of water resources development in Eastern Nile Basin shall explore opportunitiesrnusing probabilistic approaches under various level of regional cooperation scenarios.